Spinous process implants and associated methods

ABSTRACT

The present invention provides spinous process implant and associated methods. In one aspect of the invention the implant limits the maximum spacing between the spinous processes. In another aspect of the invention, a spacer has at least one transverse opening to facilitate tissue in-growth. In another aspect of the invention, an implant includes a spacer and separate extensions engageable with the spacer. In another aspect of the invention, instrumentation for inserting the implant is provided. In other aspects of the invention, methods for treating spine disease are provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/934,604, filed Nov. 2, 2007, which claims the benefit ofU.S. Provisional Application No. 60/912,273, filed Apr. 17, 2007 andU.S. Provisional Application No. 60/884,581, filed Jan. 11, 2007, all ofwhich are hereby incorporated by reference in their entirety. Thisapplication further claims the benefit of U.S. Provisional ApplicationNo. 61/165,354, filed Mar. 31, 2009, which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to spinous process implants and associatedmethods.

BACKGROUND

The vertebrae of the human spine are arranged in a column with onevertebra on top of the next. An intervertebral disc lies betweenadjacent vertebrae to transmit force between the adjacent vertebrae andprovide a cushion between them. The discs allow the spine to flex andtwist. With age, spinal discs begin to break down, or degenerateresulting in the loss of fluid in the discs and consequently resultingin them becoming less flexible. Likewise, the disks become thinnerallowing the vertebrae to move closer together. Degeneration may alsoresult in tears or cracks in the outer layer, or annulus, of the disc.The disc may begin to bulge outwardly. In more severe cases, the innermaterial of the disc, or nucleus, may actually extrude out of the disc.In addition to degenerative changes in the disc, the spine may undergochanges due to trauma from automobile accidents, falls, heavy lifting,and other activities. Furthermore, in a process known as spinalstenosis, the spinal canal narrows due to excessive bone growth,thickening of tissue in the canal (such as ligament), or both, in all ofthese conditions, the spaces through which the spinal cord and thespinal nerve roots pass may become narrowed leading to pressure on thenerve tissue which can cause pain, numbness, weakness, or even paralysisin various parts of the body. Finally, the facet joints between adjacentvertebrae may degenerate and cause localized and/or radiating pain. Allof the above conditions are collectively referred to herein as spinedisease.

Conventionally, surgeons treat spine disease by attempting to restorethe normal spacing between adjacent vertebrae. This may be sufficient torelieve pressure from affected nerve tissue. However, it is oftennecessary to also surgically remove disc material, bone, or othertissues that impinge on the nerve tissue and/or to debride the facetjoints. Most often, the restoration of vertebral spacing is accomplishedby inserting a rigid spacer made of bone, metal, or plastic into thedisc space between the adjacent vertebrae and allowing the vertebrae togrow together, or fuse, into a single piece of bone. The vertebrae aretypically stabilized during this fusion process with the use of boneplates and/or pedicle screws fastened to the adjacent vertebrae.

Although techniques for placing intervertebral spacers, plates, andpedicle screw fixation systems have become less invasive in recentyears, they still require the placement of hardware deep within thesurgical site adjacent to the spine. Recovery from such surgery canrequire several days of hospitalization and long, slow rehabilitation tonormal activity levels.

More recently, investigators have promoted the use of motionpreservation implants and techniques in which adjacent vertebrae arepermitted to move relative to one another. One such implant that has metwith only limited success is the artificial disc implant. Thesetypically include either a flexible material or a two-piece articulatingjoint inserted in the disc space. Another such implant is the spinousprocess spacer which is inserted between the posteriorly extendingspinous processes of adjacent vertebrae to act as an extension stop andto maintain a minimum spacing between the spinous processes when thespine is in extension. The spinous process spacer allows the adjacentspinous processes to move apart as the spine is flexed.

SUMMARY

The present invention provides a spinous process implant and associatedmethods.

In one aspect of the invention, an implant for placement between spinousprocesses of adjacent vertebrae includes a spacer and an extension. Thespacer has a sidewall with superior and inferior surfaces operable toabut the spinous processes and maintain the spinous processes in spacedapart relationship. In one example, the sidewall extends generallyparallel to a longitudinal axis. In other examples, the sidewall mayconverge, diverge, or define any other suitable shape relative to alongitudinal axis. The sidewall may be cylindrical, tapered,symmetrical, and/or asymmetrical relative to a longitudinal axis. Theextension projects from the spacer transverse to the longitudinal axisto lie generally alongside the spinous processes of adjacent vertebraeand engage the spinous processes to limit the maximum spacing betweenthe spinous processes.

In another aspect of the invention, the extension includes an adjustablefastener.

In another aspect of the invention, the extension includes a removablefastener.

In another aspect of the invention, an implant for placement betweenspinous processes of adjacent vertebrae includes a spacer having atleast one transverse opening communicating from at least one of asuperior and inferior outer surface inwardly to facilitate tissuein-growth.

In another aspect of the invention, the spacer includes a hollowinterior and a plurality of transverse openings communicating from thesuperior and inferior outer surfaces to the hollow interior tofacilitate tissue growth.

In another aspect of the invention, the spacer includes a porousstructure and the transverse openings comprise a plurality of pores.

In another aspect of the invention, an implant for placement betweenspinous processes of adjacent vertebrae of a spine includes a spacer andseparate extensions engageable with the spacer at its ends. The spaceris provided in a variety of lengths and superior to inferior surfacespacings:

In another aspect of the invention, an implant for placement betweenspinous processes of adjacent vertebrae of a spine includes a spacer anda cerclage element. The cerclage element is offset posteriorly of themidline in use so that the spacer defines a fulcrum and the cerclageelement is extendible around a portion of a vertebra and operative toimpart a moment to the vertebra about the spacer.

In another aspect of the invention, instrumentation includes twoinstruments each having a working portion tapering from a largercross-sectional dimension nearer a handle to a smaller cross-sectionaldimension near the free end. The free end of one of the instrumentsdefines a hollow tip sized to engage the free end of the firstinstrument and sized to engage the hollow tip of the implant.

In another aspect of the invention, a method includes inserting a spacerbetween spinous processes of adjacent vertebrae to provide both anextension stop and a flexion stop.

In another aspect of the invention, a method includes inserting a spacerbetween spinous processes of adjacent vertebrae and connecting acerclage element to the adjacent vertebrae to impart a moment to thevertebrae about the spacer.

In another aspect of the invention, a method includes inserting atapered instrument between adjacent spinous processes; engaging a tip ofa spinous process spacer with the tip of the tapered instrument andpassing the engaged pair back between the adjacent spinous process toinsert the spacer between the spinous processes.

In another aspect of the invention, extensions may be provided that areshaped to allow extensions on adjacent implants to interleave.

In another aspect of the invention, extensions may be provided thatpermit an extension of one implant to overlie an extension of anadjacent implant.

In another aspect of the invention, an implant for placement betweenspinous processes may be shaped to accommodate a small or missingspinous process such as, e.g., on the sacrum of a patient.

In another aspect of the invention, an implant for placement betweenspinous processes may include a spacer that has a variable height.

In another aspect of the invention, an implant for placement betweenspinous processes may include a mechanism operable to distract adjacentspinous processes away from one another.

In another aspect of the invention, an implant for placement betweenspinous processes may include bone gripping extensions and a mechanismoperable to simultaneously lock a desired horizontal spacing betweenextensions on opposing sides of a single spinous process and a desiredvertical spacing between extensions engaged with adjacent spinousprocesses.

In another aspect of the invention, an implant for placement betweenspinous processes may include a spacers and/or extensions engageablewith more than two spinous processes to constrain the motion of multiplespinal levels.

In another aspect of the invention, an implant for placement betweenspinous processes may include first and second spacers. The first andsecond spacers may be made of different materials.

BRIEF DESCRIPTION OF THE DRAWINGS

Various examples of the present invention will be discussed withreference to the appended drawings. These drawings depict onlyillustrative examples of the invention and are not to be consideredlimiting of its scope.

FIG. 1 is a cross sectional view of an implant according to the presentinvention in situ;

FIG. 2 is a side elevational view of the implant of FIG. 1 in situ;

FIG. 3 is a an exploded perspective view of the implant of FIG. 1;

FIG. 4 is a front elevational view of the implant of FIG. 1;

FIG. 5 is a back elevational view of the implant of FIG. 1;

FIG. 6 is a top plan view of the implant of FIG. 1;

FIG. 7 is a front elevational view of the implant of FIG. 1 showing theassembly in an alternate position;

FIG. 8 is a side elevational view of the implant of FIG. 1;

FIG. 9 is a perspective view of a pair of implants like that of FIG. 1in situ;

FIG. 10 is a cross sectional view of an implant like that of FIG. 1illustrating an alternate material and cerclage elements;

FIGS. 11-13 are side elevational views of an implant like that of FIG. 1shown in use with cerclage elements;

FIGS. 14-24 are perspective views of alternative embodiments of theinvention;

FIG. 25 is a perspective view of instrumentation for implanting theimplant of FIG. 1;

FIG. 26 is a perspective view of the instrumentation of FIG. 25 in useto implant the implant of FIG. 1.

FIGS. 27-58 are perspective views of aspects of the invention.

DESCRIPTION OF THE ILLUSTRATIVE EXAMPLES

Embodiments of spinous process implants according to the presentinvention include a spacer and an extension extending outwardly from thespacer. The spinous process implant May be configured for insertionbetween adjacent spinous processes of the cervical, thoracic, and/orlumbar spine. The spacer may be provided in a variety of sizes toaccommodate anatomical variation amongst patients and varying degrees ofspace correction. The spacer may include openings to facilitate tissuein-growth to anchor the spacer to the vertebral bodies such as tissuein-growth from the spinous processes. The spacer may be configured fortissue in-growth from superior and inferior spinous processes to causefusion of the adjacent spinous processes. The openings may be relativelylarge and/or communicate to a hollow interior of the spacer. A hollowinterior may be configured to receive bone growth promoting substancessuch as by packing the substances into the hollow interior. The openingsmay be relatively small and/or comprise pores or interconnecting poresover at least a portion of the spacer surface. The openings may befilled with bone growth promoting substances.

The spacer may have any suitable cross-sectional shape. For example, itmay be cylindrical, D-shaped, C-shaped, H-shaped, include separatedcantilevered beams, and/or any other suitable shape. The shape mayinclude chamfers, fillets, flats, relief cuts, and/or other features toaccommodate anatomical features such as for example the laminae and/orfacets. The spacer may have a sidewall that is generally parallel,tapered, or irregularly shaped. The spacer may have a fixed height or itmay have a variable height allowing for adjustment intraoperatively. Asingle spacer may be provided for a single level of spine correction ormultiple spacers may be provided for a single level or multiple levelsof spine correction. Where multiple spacers are provided, they may bemade of the same or different materials.

The extension may extend transversely from the spacer relative to aspacer longitudinal axis to maintain the spacer between adjacent spinousprocesses. A single extension may extend in one or more directions ormultiple extensions may be provided that extend in multiple directions.One or more extensions may be adjustable longitudinally relative to oneanother and/or the spacer to allow the extensions to be positionedrelative to the spinous processes. A moveable extension may be providedthat is movable axially relative to the spacer and another extension.Alternatively, a plurality of moveable extensions may be provided. Forexample, the extensions may clamp against the sides of the spinousprocesses to immobilize the spinous processes relative to one anotherand promote fusion between the adjacent vertebrae. The extensions mayinclude fasteners engageable with the spinous processes. The fastenersmay include sutures, wires, pins, straps, clamps, spikes, screws, teeth,adhesives, and/or other suitable fasteners. The fasteners may beintegrated into the extensions or they may be modular. Modular fastenersmay be adjustable, replaceable, and/or removable to allow tailoring ofthe kind and quality of fixation from rigid fixation to no fixation.

Extensions may be provided that permit an extension of one implant tooverlie, or overlap, an extension of an adjacent implant. For example,the extensions may overlap similar to shingles overlapping. Theextensions may be offset to further facilitate the overlapping ofadjacent extensions. The extensions may have smooth surfaces thatfacilitate relative motion between overlapping portions of extensions.The extensions may have surfaces that engage one another to resistrelative motion; for example, opposing surfaces of overlappingextensions may include pads, hooks, pins, teeth, bristles, surfaceroughness, adhesive, holes, loops, screws, bolts, and/or other featuresthat permit one extension to grip another.

The implant may be shaped to accommodate a small or missing spinousprocess such as, for example, on the sacrum of a patient. For example, aportion of one or more extensions may flare outwardly to seat on arelatively broader and/or flatter portion of a bone such as the sacrum.Such an extension may include fasteners that are longer, sharper, and/orotherwise adapted to penetrate and grip the bone. The extensions may beangularly variable relative to one another to accommodate the shape ofthe underlying bone.

The spacer may have a fixed height or a variable height. A variableheight spacer may include a first portion and a second portion having avariable height spacing that may be locked at a desired relativespacing. The height spacing may be adjustable and/or lockablesimultaneously with or independently from a horizontal bone grippingspacing of the extensions. The height spacing may be adjustable byexerting a spacing force on a first and second portion with a removableinstrument and then locking the desired spacing. The height spacing maybe adjustable by operation of a mechanism incorporated into the implantitself. The height spacing may be adjustable and the desired spacinglocked by a single mechanism. Height spacing adjustment of the spacermay be used to distract adjacent spinous processes away from oneanother.

The implant may include a mechanism for compressing and/or distractingextensions toward or away from one another while they are engaged withthe bone of adjacent spinous processes such that the adjacent spinousprocesses are similarly compressed or distracted away from one another.

The implant may include spacers and/or extensions engageable with morethan two spinous processes to treat multiple spinal levels.

The spacer, extensions, and/or fasteners may advantageously be made ofdifferent materials. For example, the spacer and extensions may be madeof a relatively softer material while the fasteners may be made of arelative harder material. For example, the spacer and/or extension maybe made of a polymer and/or other relatively soft material and thefastener may be made of a metal and/or other relatively hard material.The different materials may have different transmission properties suchthat one may appear well defined on a medical image and the other appearonly dimly or not at all. For example, a metal portion of an implantwill show plainly on an x-ray whereas a polymer portion will be muchfainter. These properties can be used to allow a surgeon to see thatcertain portions, e.g. fasteners are engaged with bone while allowing aclear view through other portions to visualize the treatment site, e.g.,the space between bones.

Cerclage may be used to stabilize the spinous process implant and/or toprovide other benefits. For example, wires, straps, bands, cables,cords, and/or other elongated members may encircle the pedicles,laminae, spinous processes, transverse processes, and/or other spinalstructures. The cerclage may be relatively inextensible to provide ahard check to spine flexion or the cerclage may be relatively extensibleto provide increasing resistance to flexion. The cerclage may berelatively flexible and drapeable such as a woven fabric or it may berelatively rigid such as a metal band. The cerclage may have shapememory properties that cause it to resume a prior set shape afterimplantation. The cerclage may be independent of the spinous processimplant or may engage it. For example, the cerclage may pass through ahollow interior of the spinous process implant and/or engage theextension. The cerclage may be offset from the spacer and provide atensioning force that uses the spacer as a fulcrum to offload the discand/or open the disc space.

The implant may be supplemented with bone growth promoting substances tofacilitate fusion of adjacent vertebrae between spinous processes,laminae, transverse processes, facets, and/or other spinal structures.The bone growth promoting substances may be spaced from the implant,placed adjacent the implant, sandwiched between the implant andunderlying bone placed inside the implant, coated onto the implant,and/or otherwise placed relative to the implant. If it is coated ontothe implant it may cover the entire implant or only selected portions ofthe implant such as the extensions, fasteners, spinous processcontacting portions of the spacer, and/or other portions.

In addition, bone growth promoting substances may include structuralmembers that contribute directly to the support of the spacing betweenadjacent vertebrae. For example, a structural bone graft may beincorporated into, onto, around, and/or otherwise associated with thespacer and/or extensions to both provide structural support and ascaffold for new bone formation. For example, a structural piece of bonemay engage with the spacer and extend beyond the spacer such thatadjacent spinous processes rest on the structural bone.

As used herein, bone growth promoting substances may include bone paste,bone chips, bone strips, structural bone grafts, platelet derived growthfactors, bone marrow aspirate, stem cells, bone growth proteins, bonegrowth peptides, bone attachment proteins, bone attachment peptides,hydroxylapatite, calcium phosphate, other ceramics, and/or othersuitable bone growth promoting substances.

The implant and any associated cerclage or other components may be madeof any suitable biocompatible material including among others metals,resorbable ceramics, non-resorbable ceramics, resorbable polymers, andnon-resorbable polymers. Some specific examples include stainless steel,titanium and its alloys including nickel-titanium alloys, tantalum,hydroxylapatite, calcium phosphate, bone, zirconia, alumina, carbon,bioglass, polyesters, polylactic acid, polyglycolic acid, polyolefins,polyamides, polyimides, polyacrylates, polyketones, fluropolymers,and/or other suitable biocompatible materials and combinations thereof.

The spinous process implant may be used to treat spine disease in avariety of surgical techniques including superspinous ligamentsacrificing posterior approaches, superspinous ligament preservingposterior approaches, lateral approaches, and/or other suitableapproaches. The spinous process implant may be used to treat spinedisease by fusing adjacent vertebrae or by preserving motion betweenadjacent vertebrae. It may include only an extension stop such as aspacer, only a flexion stop such as flexible cerclage elements, or botha flexion and extension stop. The spinous process implant may be used toreduce loads on the facet joints, increase spinous process spacing,reduce loads on the disc, increase anterior disc spacing, and/orotherwise treat spine disease. Anterior effects may be accomplished bytensioning spine elements posterior to the spacer to apply a mechanicaladvantage to the spinal construct. Techniques for the spinal processimplant may include leaving the tissues at the surgical site unmodifiedor modifying tissues such as trimming, rasping, roughening, and/orotherwise modifying tissues at the implant site.

FIGS. 1 and 2 depict posterior and lateral views of a pair of adjacentvertebrae of the lumbar spine 10. A superior vertebra 12 is separatedfrom an inferior vertebra 14 by a disc 16. Each vertebra includes a pairof transverse processes 18, 19, a posteriorly projecting spinous process20, 21, and a pair of laminae 22, 23 connecting the transverse processes18, 19 to the spinous process 20, 21. In addition to the connectionthrough the disc 16, the vertebrae 12, 14 articulate at a pair of facetjoints 24.

FIGS. 1-9 illustrate an exemplary spinous process implant 100. Theimplant 100 includes a spacer 102 positioned between the spinousprocesses 20, 21. The height 104 of spacer 102 limits how closely thespinous processes 20, 21 can move together. Thus, the spacer 102maintains a minimum distance between the spinous processes 20, 21. Inthe case of spine disease involving posterior subsidence of the adjacentvertebra, insertion of the spacer 102 between the spinous processes 20,21 will move the vertebrae apart and relieve pressure on nerve tissueand the facet joints 24.

As shown in FIG. 3, the spacer 102 includes a first end 106, a secondend 108, and a longitudinal axis 110 extending from the first end to thesecond end. In the illustrated example, the spacer 102 has a sidewall112, generally parallel to the longitudinal axis 110, including superiorand inferior outer surfaces 114, 116. Transverse openings 118 (see alsoFIG. 6) communicate from the superior and inferior outer surfaces 114,116 inwardly to facilitate tissue in-growth. The exemplary spacer 102includes a hollow interior 120 bounded by an inner surface 122 such thatthe openings 118 communicate from the outer surface to the hollowinterior 120. Bone growth promoting substances 124 are shown packed intothe hollow interior 120 in FIGS. 1 and 2 to promote fusion of thevertebrae 12, 14 by bone growth between the spinous processes 20.

The spinous process implant 100 further includes a first extension 126projecting outwardly from the spacer 102 transverse to the longitudinalaxis 110 to lie generally alongside the superior spinous process.Abutment of the first extension 126 with the spinous process 20 helps tomaintain the spacer 102 between the spinous processes 20. In theexemplary spinous process implant 100, the first extension 126 is fixedrelative to the spacer 102 and the implant includes a second extension128 mountable to the spacer for axial movement relative to the firstextension 126. The second extension 128 may be moved toward the firstextension 126 to approximate the width of the spinous process 20 andbetter stabilize the implant 100. It is fixed in place by tightening aset screw 130 against the spacer 102. The extensions 126, 128 includefasteners 132, 134, 136 projecting from the extensions 126, 128 toengage the spinous process 20 to fix the spacer 102 to the spinousprocess 20. FIG. 1 depicts additional bone growth promoting substance inthe form of a strips of bone 125 sandwiched between the extensions 126,128 along the sides of the spinous processes 20 to promote bone growthalong the sides of the spinous processes to further inhance fusion ofthe vertebrae 12, 14. The extensions 126, 128 preferably extendinferiorly (as shown) as well as superiorly to optionally attach to theinferior spinous processes to immobilize the spinous processes 20relative to one another while fusion takes place.

The fasteners 132, 134, and 136 may take any suitable form. They may bemade integral with the extensions 126, 128 such as by machining orcasting them with the extensions or they may be formed separately andpermanently attached to the extensions 126, 128. Fastener 132 is asharpened spike that threadably engages the extension 126. The threadedengagement allows the fastener 132 to be replaced with a differentfastener 132. For example, the fastener 132 may be replaced by one thathas a different shape, a different size, a different material, or adifferent surface coating. The threaded engagement also allows thefastener 132 to be adjusted to extend by varying amounts from theextension 126 to vary how it engages the bone. Thus, the fastener 132can be adjusted to fit differently shaped bones or to penetrate into abone by varying amounts. For example, multiple threaded fasteners 132can be adjusted to extend by different amounts to conform to curved orangled bone. Finally, the threaded engagement allows the user to removethe fastener 132 when fixation is not desired such as when it is desiredto use implant 100 in a non-fusion procedure as an extension stopwithout limiting flexion.

Fasteners 134 and 136 are provided as multi-spike pods allowing aplurality of spikes to be quickly adjusted, changed, or omitted.Fastener 134 includes a non-circular tab 138 engageable with anon-circular opening 140 in the extension 126. The non-circularengagement prevents the fastener 134 from rotating. The tab 138 may forma press-fit, snap-fit, or other suitable engagement with the opening140. The tab 138 may be further secured by a supplemental screw 142.Fastener 136 includes a threaded shaft 144 threadably engaged with abase member 146 to allow the length of the fastener 136 to be adjusted.The shaft 144 engages the extension 126 in rotating and pivoting mannersuch that the fastener 136 can be adjusted rotationally and angularly toengage the bone surface. In the illustrative embodiment, the shaft 144terminates in a spherical ball 148 that engages the opening 140 in aball-and-socket arrangement for three degrees of freedom. However, anymechanism that allows any number of degrees of freedom may be used. Thefastener 136 may be allowed to move in use so that as the extension 126is pressed toward a bone the fastener 136 adjusts to the angle of thebone surface. The fastener 136 may also be secured such as by screw 142to adjust the tension in the joint and/or to lock the fastener 136 in apredetermined orientation.

FIG. 4 illustrates the axial relationship of fasteners on the opposingextensions 126, 128. In the illustrative implant 100, the fasteners 132at the top of the implant 100 are shown aligned along a common axis 150.The fasteners 134 at the bottom of the implant 100 are shown offset sothat they can interleave if necessary as they are pressed into a bone.Any combination of fastener type, number, and alignment may be providedon the implant 100.

As seen in FIGS. 5 and 6, the ends 106, 108 of the spacer 102 includeanterior chamfers 152. These chamfers 152 allow the ends 106, 108 toclear posteriorly facing structures of the vertebrae 12, 14 such as thefacet joints 24. Also, as seen in FIGS. 5 and 6, the spacer 102 isoffset anteriorly relative to the extensions 126, 128 such that thelongitudinal axis 110 of the spacer 102 is anterior of the midline 154of the extensions 126, 128. The anterior offset of the spacer 102 allowsit to fit deeply between the spinous processes 20, 21 while theextensions 126, 128 fit alongside the spinous processes 20, 21.

As best seen in FIGS. 3 and 8, the second extension 128 defines anaperture 155 conforming generally to the cross-sectional shape of thespacer 102. In the illustrative embodiment of FIGS. 1-9, the aperture155 opens anteriorly to form a “C”-shape. Tabs 156 extend inwardly fromthe superior and inferior portions of the aperture to slidingly engageelongated slots 158 in the superior and inferior surfaces of the spacer102. The second extension 128 can be translated longitudinally towardand away from the first extension 126. Tightening the set screw 130against the posterior side 160 of the spacer 102 forces the tabs 156posteriorly against the sides of the slots 158 and locks the secondextension 128 in place longitudinally. The posterior side 160 of thespacer 102 may be roughened as shown to better grip the set screw 130.The set screw 130 may also dig into the surface of the spacer 102 upontightening to positively grip the spacer 102. The aperture 155 mayconform closely to the spacer 102 to constrain the second extension 128to generally parallel motion relative to the first extension 126.Alternatively, the aperture 155 may be larger than the spacer 102 by apredetermined amount to permit a predetermined amount of angularadjustment of the second extension 128 relative to the first extension126 as shown in FIG. 7 to allow the extension 128 to adjust to theunderlying bone surface.

As best seen in FIG. 8, the second extension 128 includes a first lobe161 having a first lobe centerline 162 and a second lobe 164 having asecond lobe centerline 166. In the illustrative embodiment, the firstlobe centerline 162 and the second lobe centerline 166 are parallel andspaced apart so that the second extension 128 has a generally “Z”-shapedplan form. This shape allows the extension of one implant 100 tointerleave, if necessary, with another implant 100 in a multilevelsurgery as shown in FIG. 9 to permit close spacing of the implants,and/or longer extension lobes for more extensive bone engagement. In theillustrative embodiment of FIGS. 1-9, the centerlines 162 and 166 areoffset equidistantly from the midline 154 of the second extension 128.The centerlines 162 and 166 may vary from parallel and they may beoffset asymmetrically to form different shapes to accommodate differentvertebral anatomy. For example, the shape may be tailored for differentportions of the spine 10. In the illustrative embodiment of FIGS. 1-9,the first extension 126 has the same shape as the second extension 128.However, the shape may be varied between the first and second extensions126, 128.

FIG. 10 depicts an implant 200 having a spacer 202 and first and secondextensions 204, 206. The spacer 202 includes pores 208 for tissue togrow into. The pores 208 may be individual openings spaced from oneanother, interconnecting openings, or combinations of individual andinterconnecting openings. The spacer 202 may be a monolithic blockhaving uniform porosity throughout. Alternatively, the spacer 202 mayinclude an outer porous layer 210 and an inner layer 212 of differentcomposition. For example, the inner layer 212 may be solid, porous,hollow, or some other configuration. A porous inner layer may have poresof a different size and/or distribution than the outer layer 210.Similarly, any porous portion may have uniform porosity or porosity thatvaries in pore size or density. A variety of pore configurations aresuitable. Preferably the pore size is in the range of 1 μm to 2 mm. Morepreferably, the pore size is in the range of 1 μm to 500 μm. Still morepreferably, the pore size is in the range of 75 μm to 300 μm. The poresmay be produced by a variety of processes such as sintering ofparticles; leaching a soluble component from the material; matting,weaving, or otherwise combining fibers: and/or by any other knownprocess. The pore size may be tailored to preferentially promote hardtissue growth, soft tissue growth, or a combination of hard and softtissue growth. The extensions 204, 206 may be solid or they may havelarge and/or small openings to encourage bone growth in and/or aroundthe extensions 204, 206. The spacer 202 and/or extensions 204, 206 mayalso be coated as previously described.

The extensions 204, 206 may be fixed and/or adjustable. In theillustrative implant 200 of FIG. 10, the first extension 204 is fixed toone end of the spacer 202 and the second extension 206 is translatablealong the spacer 202 to allow the extensions to be placed adjacent thespinous processes. The extensions 204, 206 are shown with optionalspikes 214 that may engage the spinous processes 20, 21 to fix thespinous processes 20, 21 relative to one another.

FIG. 10 also depicts the use of cerclage in conjunction with the implant200. For example, one or more flexible bands 216 are placed around thelamina 22, 23 to provide a flexion stop. The band 216 may help carry theload exerted on the spikes 214 during spine flexion. Alternatively or inaddition to the band 216, one or more bands 218, 220 may be placedaround the transverse processes 18, 19.

FIGS. 11-13 depict additional examples of the use of cerclage inconjunction with a spinous process implant 300 according to the presentinvention. The implant includes a spacer 302 for placement betweenadjacent spinous processes 20, 21 and an extension 304. In the exampleof FIG. 11, a band 310 of flexible material is looped around the spinousprocesses 20, 21. By placing the band 310 behind the areas 312, 314where the spinous processes contact the spacer 302 an offset 318 iscreated. Tightening of the band 310 creates a moment 320, 322 on eachvertebra 12, 14 that offloads some of the pressure on the disc 16between the adjacent vertebrae 12, 14. With increased tightening of theband 310, the anterior spacing 324 of the vertebrae 12, 14 may actuallybe increased. Thus; by using the spinous process implant 300 incombination with the band 310, the vertebrae 12, 14 may be levered apartwith the implant 300 being used as the fulcrum. In addition to theadvantages already mentioned, this combination produces an anterior discspace effect with a posterior spinous process procedure that is lessinvasive than typical disc spacing procedures.

In the examples of FIGS. 12 and 13, the implant 300 includes a mechanismfor attaching the cerclage band 310 to the implant 300. In the exampleof FIG. 12, the mechanism includes openings 330, 332 in the superior andinferior ends of the extension 304. By attaching the band 310 to theextension 304, the band 310 and extension 304 help stabilize one anotheragainst anterior-posterior displacement. This attachment also helpsposition the band 310 at a predetermined offset 318 from the spacer 302.In the example of FIG. 13, the band 310 is looped through a hollowinterior of the spacer 302 itself. In this example, the band is notoffset and produces minimal or no moment on the vertebrae.

FIGS. 14-24 illustrate alternative mechanisms for attaching a movableextension to the implant of FIG. 1. Referring to FIG. 14, an implant 400includes a spacer 402, a first extension 404 and a second, movableextension 406. The movable extension 406 includes a body in the form ofa ring 408 with an inner surface 410 generally conforming to the outersurface of the spacer 402 so that the ring is slidingly receivable onthe spacer 402. A set screw 412 is tightened against the spacer 402 tofix the movable extension 406 at a desired position on the spacer 402.Tightening of the set screw 412 biases the movable extension 406posteriorly relative to the spacer 402. The anterior portion 414 of thering presses against the anterior portion 416 of the spacer 402 tocounter this posterior bias and allow the set screw 412 to lock theextension 406. The spacer 402 may include a plurality of indentations418 to create a positive engagement with the set screw 412 atpredetermined axial locations. The ring 408 may be sized to permit apredetermined amount of tilting of the extension 406 relative to thespacer 402.

Referring to FIG. 15, an implant 500 includes a spacer 502, a firstextension 504, and a second, movable extension 506. The spacer 502includes a plurality of cantilevered beams 508, 510 projecting parallelto a longitudinal axis 512 away from the first extension 504. In theexample of FIG. 15, the spacer 502 includes a pair of opposed “C”-shapedbeams 508, 510 with their concave surfaces directed inwardly. The spacer502 includes openings 514 through the beams 508, 510 and defineselongated openings 516, 518 anteriorly and posteriorly between thebeams. The movable extension 506 includes a body in the form of aninterrupted ring 520. The ring 520 is open anteriorly and the margins ofthe opening define posteriorly directed hooks 522, 524. The innersurface 526 of the ring conforms generally to the outer surface of thebeams 508, 510 so that the ring is slidingly receivable on the spacer502. The open anterior configuration of the ring 520 provides clearanceto ease sliding of the ring in-vivo. A set screw 528 is tightenedagainst the spacer 502 to fix the movable extension 506 at a desiredlongitudinal position on the spacer. The hooks 522, 524 curve around aportion of the anterior edge of the beams 508, 510 to resist posteriortranslation of the ring relative to the spacer 502 when the set screw528 is tightened.

Referring to FIG. 16, an implant 600 is depicted that is similar toimplant 500 of FIG. 15 having a spacer 602, first extension 604, andmovable extension 606. However, the ring 608 is truncated anteriorly toprovide even more anterior clearance than the ring 520 of FIG. 15. Thering 608 includes a key 610 projecting anteriorly from the posteriorside of the ring 608 and expanding superiorly and inferiorly to engagethe inner surface 612 of the beams 614, 616 to resist posteriortranslation of the ring relative to the spacer 602. The key 610 alsopartially blocks the hollow interior 618 of the spacer 602 to helpretain material optionally packed into the interior 618.

Referring to FIG. 17, an implant 700 includes a spacer 702, a firstextension 704, and a second movable extension 706. The spacer 702includes a sidewall 708 defining an outer surface 710 and an innersurface 712. In the example of FIG. 17, the spacer 702 is generally inthe shape of a hollow flattened cylinder with a “D”-shaped crosssection. However, the spacer 702 could be any desirable shape. Thespacer 702 includes a plurality of openings 714 communicating from theouter surface 710 to the inner surface 712. The movable extension 706includes a projection 716 configured generally like the spacer 702 butbeing sized to slide within the spacer 702 in telescoping relationship.The projection (or the spacer) may optionally include one or morefixation mechanisms to lock the extensions 704, 706 at a desiredlongitudinal spacing. Fixation mechanisms may include a set screw 718, aridge 720 forming a snap fit with a groove 722 or other feature, adetent 724 engageable with openings 714, and/or other suitable fixationmechanisms. Any one or combinations of these mechanisms may be used andthey may be reversed from the orientation shown.

Referring to FIGS. 18-20, an implant 800 includes a spacer 802, a firstextension 804, and a second, movable extension 806. The spacer 802includes a plurality of cantilevered beams similar to FIGS. 15 and 16except that in this example there are three beams 808, 810, 812. Thebeams project parallel to a longitudinal axis 814 away from the firstextension 804. In the example of FIG. 18, the anterior beam 812 includesa posteriorly opening groove 816. The posterior beams 808, 810 andanterior beam 812 define an elongated slot 818 between them openingsuperiorly and inferiorly. The posterior beams 808, 810 further definean elongated slot 820 between them opening posteriorly. FIG. 20illustrates a cruciform opening 822 defined by the projection of thegroove 816 and slots 818, 820 projected through the first extension 804.The movable extension 806 includes a body 824 sized to slidingly engagethe slot 818. An optional lug 826 can project anteriorly into groove 816to constrain tilting of the movable extension 806 relative to the firstextension 804. The lug 826 can be sized to lit closely within groove 816to prevent tilting of the movable extension 806 or it can be sizedsmaller than the groove 816 to permit a predetermined amount of tilt. Aset screw 828 is provided to lock the movable extension 806 to thespacer 802.

Referring to FIG. 21, an implant 900 is depicted that is configuredgenerally like that of FIG. 16. However, an end wall 902 adjacent thefirst extension 904 includes a through bore 906 and the movableextension 908 includes a key 910 with a through bore 912. The bores 906,912 receive a fastener to fix the extensions 904, 908 at a maximumspacing to prevent them from moving apart. Fasteners may include screws,bolts, nuts, cables, wires, ties, rods, and/or any other suitablefastener. In the example of FIG. 21, the fastener includes an elongatedcrimp receiving member 914, such as a cable, and crimp members 916, 918,such as ferrules or compressible beads.

Referring to FIG. 22, an implant 1000 includes a spacer 1002, a firstextension 1004, and a second extension 1006. The spacer 1002 includes anouter surface 1008 defining one or more longitudinal grooves 1010extending along the outer surface 1008 and through the first extension1004. The first extension 1004 includes one or more corresponding slots1012 having a radially outwardly extending portion 1014 through thefirst extension 1004 and communicating with the grooves 1010. The slots1012 have a radially inwardly extending portion 1016 defining a shoulder1018 at the end of the grooves 1010. The second extension 1006 includesone or more corresponding projections 1020 projecting longitudinallytoward the first extension 1004 and terminating at a radially inwardlydirected tab 1022. The second extension 1006 further includes acentering bore 1024 having conical opening engageable with a conicalfree end 1026 of the spacer 1002. The second extension 1006 is attachedto the spacer 1002 by pressing the tabs 1022 against the conical end1026 of the spacer 1002 to spread the projections outwardly until thetabs 1022 engage the grooves 1010. The tabs 1022 are slid along thegrooves 1010 until they exit through the slots 1012 and the tabs 1022snap inwardly over the shoulders, 1018 and into the portions 1016.Abutment of the tabs 1022 against the shoulders 1018 prevents the firstand second extensions 1004, 1006 from moving apart. The engagement ofthe conical end 1026 of the spacer 1002 with the bore 1024 providesradial stability to the assembly.

Referring to FIG. 23, an implant 1100 includes a spacer 1102, a firstextension 1104, and a second extension 1106. The spacer 1102 includes atransverse groove 1108 with a central boss 1110 having an enlarged head1112. The second extension 1106 includes a portion 1114 sized to fitwithin the groove 1108 and an opening 1116 bordered by one or moreangled tabs 1118. The second extension 1112 is assembled to the spacerby pressing the portion 1114 into the groove 1108 with the central boss1110 directed into the opening 1116. As the boss 1110 is pressed throughthe opening 1116, the tabs 1118 flex outwardly to allow it to pass. Oncethe boss 1110 is past the tabs 1118, the tabs 1118 return to theiroriginal position and snap behind the enlarged head 1112. In thisconfiguration, the boss 1110 retains the second extension 1106longitudinally and the groove 1108 prevents the second extension 1106from rotating about the longitudinal axis of the implant 1100.

Referring to FIG. 24, an implant 1200 includes a spacer 1202, a firstextension 1204, and a second extension 1206. The spacer 1202 includes asolid cylindrical sidewall 1208 defining a hollow interior 1210. Theextensions 1204, 1206 are similarly configured and each includes aprojection 1212, 1214 sized to fit inside of the spacer 1202. Theextensions 1204, 1206 may attach to the spacer by press-fitting,snap-fitting, screwing, and/or otherwise engaging the projections 1212,1214 with the spacer 1202. Alternatively, or additionally, theextensions 1204, 1206 may attach to the spacer 1202 with any of thepreviously depicted attachment mechanisms such as with a setscrew asshown in FIG. 3 or an elongated fastener as shown in FIG. 21. In theexample of FIG. 24, the extensions 1204, 1206 are slotted longitudinallyto form flexible petals 1216 that press into the spacer 1202. Theextensions 1204, 1206 include openings 1218 to allow tissue growth,permit attachment of cerclage members, and/or receive additionalfasteners attached to the spinous processes.

The spacer 1202 of FIG. 24 could have openings as shown in some of theother examples. Likewise, the other examples could have a solid surfaceas shown in FIG. 24. Similarly the extensions of any of the examples maybe solid, have openings, or be otherwise advantageously configured.

Implants according to the present invention may be implanted using avariety of surgical approaches and techniques. Surgical approaches mayinclude superspinous ligament sacrificing posterior approaches,superspinous ligament preserving posterior approaches, lateralapproaches, and/or other suitable approaches. Techniques may includeleaving the tissues at the surgical site unmodified or modifying thetissues such as trimming, rasping, roughening, and/or otherwisemodifying them. For example, in FIG. 1, a lateral approach is used andthe inferior spinous process is cut on its superior surface 26 toenlarge the interspinous space to receive the implant 100. After theinterpinous space is prepared, the spacer 102 is inserted into theinterspinous space. If a first extension 126 is present it may bepressed inwardly to lie near or abut one or more spinous processes. If asecond extension 128 is used, it is engaged with the spacer 102 and alsooptionally pressed inwardly. In FIG. 1, opposing extensions 126, 128having inwardly directed bone fasteners have been used and pressedinwardly so that the fasteners 132 engage the spinous processes 20, 21.The engagement of the fasteners 132 with the inferior spinous process 21is not shown in FIG. 1 because the extensions are offset superiorly andinferiorly as shown in FIGS. 3, 8, and 9.

Referring to FIGS. 25 and 26, a set of instruments 1300 is provided tofacilitate lateral insertion of an implant into the interspinous space.The set of instruments includes a plurality of inserters 1302, 1303 inwhich each inserter 1302, 1303 has a first or handle portion 1304 and asecond or working portion 1306. The working portion 1306 is insertableinto the interspinous space. Preferably, the handle portion 1304 extendstransverse to the working portion 1306 to facilitate holding andmanipulating the inserter 1302, 1303 while the working portion 1306 isin the interspinous space. The handle portion 1304 and working portion1306 may define a curve, angle, offset, and/or any other suitabletransverse orientation. In the example of FIG. 25, the inserters 1302,1303 are generally “L”-shaped. The working portion 1306 tapers from arelatively larger cross-sectional dimension at a first portion 1307spaced away from its free end 1308 to a relatively smallercross-sectional dimension at its free end 1308. In the illustrativeembodiment, the working portion is conical and tapers from a largerdiameter to a smaller diameter. The end 1308 defines a hollow tip havingan opening 1310. The set of instruments 1300 is provided with aplurality of similarly configured inserters having differently sizedworking portions 1306 such that the end 1308 of one inserter 1302 willfit inside the opening 1310 at the tip of another inserter 1303.Optionally, the working portion 1306 may be separated into opposinghalves attached to opposing handles 1314, 1316. As the opposing handles1314, 1316 are moved relative to one another, the opposing halves of theworking portion 1306 move relative to one another. In the illustrativeembodiment, squeezing the handles 1314, 1316 toward one another causesthe working portion 1306 to expand as the opposing halves of the workingportion 1306 open outwardly away from one another.

In use, a first inserter 1302 is inserted into the interspinous space.The first inserter 1302 is relatively small to ease insertion. As theend 1308 is inserted further, the tapered working portion 1306 expandsthe interspinous space. Optionally, the interspinous space can befurther expanded by expanding the working portion while it is inside theinterspinous space such as by squeezing the handles 1314, 1316. Asecond, larger inserter 1302 is engaged with the first inserter 1303 byplacing its hollow tip over the tip of the first inserter 1303 and thenpassing the overlapping instruments back through the interspinous spaceto remove the first inserter 1303 and insert the second inserter 1302.As the end of the second inserter 1303 is inserted further, the taperedworking portion expands the interspinous space. Optionally, theinterspinous space can be further expanded by expanding the workingportion while it is inside the interspinous space. Progressively largerinserters can be inserted in this fashion until the interspinous spacehas been expanded to the desired size. Once the desired size has beenreached the appropriate implant size may be determined by noting thesize of the last inserter. The inserter may optionally include indicia1320 on the tapered working end corresponding to different spacer sizesto further facilitate sizing the implant. The implant is inserted byengaging the spacer 1402 with the working end of the inserter as shownin FIG. 26. The implant may be engaged inside of the hollow tip of theinserter or the tip of the inserter may engage a hollow tip on theimplant as shown. The spacer 1402 is pressed into the interspinous spaceas the inserter is withdrawn.

Referring to FIGS. 27-28, a first implant 1500 includes a spacer 1502and extensions 1504. The extensions are generally planar in theanterior-posterior plane as shown in FIG. 27, and include a superiorportion 1506, an inferior portion 1508, and spikes 1510 projectingmedially from each of the superior and inferior portions to engagespinous processes superior and inferior to the spacer 1502. Theextensions 1504 are mounted to the spacer 1502 to permit the spacingbetween the extensions to be adjusted such as by surrounding and slidingalong a portion of the spacer 1502 and to permit the spacing between theextensions to be locked such as with set screw 1503. A second implant1520 includes a spacer 1522, extensions 1524, and set screw 1523. Theextensions 1524 include a superior portion 1526 and an inferior portion1528. The inferior portion 1528 is offset laterally (outwardly) relativeto the superior portion 1526 to facilitate the inferior portion 1528overlying the superior portion 1506 of the first implant 1500 in ashingle-like arrangement. In the illustrative example, the superiorportion 1526 and inferior portion 1528 define medial surfaces 1530, 1532lying generally in planes 1534, 1536 that are generally parallel to oneanother and offset by a distance 1538. The distance 1538 is preferablyequal to at least the thickness 1540 of the superior portion 1506 of thefirst implant to allow the inferior portion 1528 of the extension 1524to lie flat against the superior portion 1506 of the extension 1504. Theoffset distance 1538 may be other values that result in an angularengagement of the inferior portion 1528 of the extension 1524 with thesuperior portion 1506 of the extension 1504. The offset may be definedby a discreet offset portion 1542 shown as a generally straight portiondefining a medial surface 1543 lying generally in a plane 1544transverse to planes 1534 and 1536. Alternatively, any one orcombination of portions 1526, 1528, and 1544, including surfaces 1530,1532, and 1543 may be flat, curved, or otherwise shaped. Likewise, theoffset may be reversed so that the extensions of first implant 1500overlie the extensions of second implant 1520.

Preferably, the inferior portion 1528 of extension 1524 includes amedially facing gripping feature and the superior portion 1506 ofextension 1504 includes a cooperating laterally facing gripping surface.In the illustrative example of FIG. 27, shown more clearly in FIG. 28,the gripping surfaces include a plurality of conical bristles 1546 ableto nest together to resist relative sliding between the extensions 1504,1524. FIG. 29 illustrates an alternative arrangement in which a spike1548 from one extension engages a hole 1550 in another extension.

In use, the first implant is placed with its spacer between adjacentspinous processes at a first spinal level and the spikes of itsextensions engaging the sides of the adjacent spinous processes. Asecond implant is then placed with its spacer between adjacent spinousprocesses at a second spinal level and the spikes at one end of itsextensions engaging the sides of a spinous process and the other endoverlying and engaging the extensions of the first implant.

Referring to FIG. 30, two implants 1570, 1580 are shown in overlappingrelationship. Implant 1570 includes a spacer 1571 and generally planarextensions 1572 having medially facing spikes 1574 and laterally facingsockets 1576. The extensions 1572 are able to engage the spacer 1571 atvariable angles. Implant 1580 likewise includes a spacer 1581 andgenerally planar extensions 1582 having medially facing spikes 1584 andlaterally facing sockets 1586. The extensions 1582 are able to engagethe spacer 1581 at variable angles. The spikes of the extensions of oneimplant are receivable in the sockets of the extensions of anotherimplant at varying angles from coaxial, or parallel, to angles as highas 45 degrees or higher. In use, one implant is placed with its spacerbetween adjacent spinous processes at a first spinal level and thespikes of its extensions engaging the sides of the adjacent spinousprocesses. A second implant is then placed with its spacer betweenadjacent spinous processes at a second spinal level and the spikes atone end of its extensions engaging the sides of a spinous process andthe spikes at another end of its extensions engaging sockets in theextensions of the first placed implant.

In the illustrative example of FIG. 30, no offset is required in theextensions to permit an overlying relationship due to the variable anglebetween the extensions and the spacers. The implants of FIG. 27 maylikewise permit variable angles between extensions and spacers. However,because of the offset of the extensions, the extensions will assume amore parallel orientation. The implants of FIGS. 27-30 may incorporatefeatures of any of the plurality of implants described throughout thisspecification.

The above described overlying implants facilitate placement of implantsat adjacent spine levels by permitting the extensions to overlap andthus the extensions require less space on the sides of the spinousprocesses. In addition, where a rigid connection is formed betweenoverlapping extensions, the rigidity of the overall spinal construct ofmultiple implants is increases. In the above described overlyingimplants, opposing surfaces of overlapping extensions may include pads,hooks, pins, teeth, bristles, surface roughness, adhesive, holes, loops,screws, bolts, and/or other features that permit one extension to gripanother.

Referring to FIGS. 31-34, an implant 1600 includes a spacer 1602 andextensions 1604. As best seen in FIG. 32, the spacer 1602 is shaped toprovide superior and inferior voids or openings 1602V. The voids oropenings 1602V are similar to the openings described throughout theapplication. The extensions 1604 include medially facing spikes 1606 forengaging the vertebrae. The spacer 1602 has a length 1608 extendingmedially-laterally and a height 1610 extending superiorly-inferiorly. Acylindrical path 1612 extends through the spacer 1602 along its length.The cylindrical path 1612 opens posteriorly through a slot 1614. A drawbolt 1616 has a spherical tip 1618 at a first end and a cylindricalthreaded portion 1620 at a second, opposite end. The tip 1618 andthreaded portion are connected by a neck 1622. The extensions 1604include threaded bores 1624 formed through the extensions 1604 in ananterior-posterior direction. The implant 1600 is assembled by threadingthe draw bolt 1616 into the extensions 1604 with the tip 1618 projectinganteriorly. The tip is slidingly engaged with the path 1612 in thespacer 1602 with the neck projecting through the slot 1614. As can beappreciated with reference to FIG.32, the spherical tip 1618 is shown inthe cylindrical path 1612. Moreover, the neck 1622 is shown extendingfrom the tip 1618 trough the slot 1614.

In use, the spacer 1602 is placed between adjacent spinous processes andthe extensions 1604 are engaged with the spacer 1602. Alternatively, oneor both extensions 1604 may be preassembled to the spacer before thespacer 1602 is inserted between adjacent spinous processes. Theextensions 1604 are pressed together to engage the spikes 1606 with thespinous processes. The fit of the spherical tip 1618 of the draw bolt1616 within the cylindrical path 1612 permits the extensions 1604 to beangled relative to the spacer 1602. If the neck 1622 of the draw bolt1616 fits closely within the slot 1614, the extensions are constrainedto angulate medially-laterally. If the neck 1622 of the draw bolt 1616fits loosely within the slot 1614, the extensions may angle bothmedially-laterally and superiorly-inferiorly. The angulation of theextensions permits them to adjust to the angle of the underlying bone.Each draw bolt 1616 is then rotated to move the corresponding extension1604 toward the spacer 1602 until the extension 1604 abuts the spacer1602. Further rotation of the draw bolt presses the extension 1604 andspacer 1602 together to lock their relative positions.

In the illustrative example of FIGS. 31-34, the extensions 1604 areflared outwardly at an inferior portion 1626. In particular, and perhapsbest seen in FIG. 31 in one exemplary embodiment, a first of theextensions 1604 may be considered to have a first planar surface 1604′defined by the superior portion 1604S. Further, the first of theextensions 1604 may be considered to have a second planar surface 1604″defined by the inferior portion 16041. A second of the extensions 1604similarly may be considered to have a third planar surface 1604′″ and acorresponding fourth planar surface 1604″″. As can be appreciated byFIG. 31, the first planar surface 1604′ and the second planar surface1604″ are non-coplanar with each other. Similarly, the third planarsurface 1604′″ and the fourth planar surface 1604″″ are non-coplanarwith each other. The outward flare directs the superior spikes outwardlyand inwardly to accommodate a small or missing spinous process such as,for example, on the sacrum of a patient. The inferior portion mayinclude one or more holes 1628 to receive screws 1630 that seat on theinferior portion and engage the inferior vertebra, such as, for example,the sacrum to more positively engage the inferior vertebra.

Referring to FIGS. 35-36, an implant 1700 includes a first half 1702 anda second half 1704. Each half 1702, 1704 includes both a portion of aspacer 1706 and an extension 1708. At least one of the spacer portionsincludes a medial-lateral slot 1710 and at least one of the extensionsincludes a superior-inferior slot 1712. When assembled, the slots 1710,1712 overlie one another and a bolt 1714 extends through the slots topin the first and second halves 1702, 1704 together. A nut 1716 capturesthe bolt 1714. The superior-inferior slot 1712 permits adjustment of thesuperior-inferior spacing between the spacer portions 1706 to vary thespacer height as can be seen by comparing FIGS. 35 and 36. Themedial-lateral slot 1710 permits adjustment of the medial-lateralspacing between the extensions 1708 to allow the extensions to beengaged with the spinous processes. When the desired spacings areachieved, the nut 1716 is tightened to compress the assembly togetherand simultaneously lock both of the spacings. In the illustrativeexample of FIGS. 35-36, the inferior portion 1718 of at least one of theextensions has angled spikes arranged to engage an inferior vertebrawith a small or missing spinous process such as the sacrum. In thisexample, one extension has spikes superiorly and inferiorly while theother extension is smooth to ease height adjustment.

Referring to FIGS. 37-38, a modular implant 1800 includes a cross bar1802 and extensions 1804. Each extension 1804 includes a spiked pad 1806with spikes 1807 projecting outwardly from the spiked pad, a spinousprocess shelf 1808 projecting outwardly in the same direction as thespikes 1807, and an extension rod 1810. The spiked pad 1806 has a width1811 and the spinous process shelf 1808 has a width 1812. In theillustrative example of FIGS. 37-38, the spinous process shelf width1812 is less than the spiked pad width 1811 to permit assembly ofaligned, opposing extensions 1804 with spinous process shelves 1808lying side-by-side in the same plane. Further, in the illustrativeexample of FIGS. 37-38, the spinous process shelf width 1812 is lessthan one-half the spiked pad width 1811 to permit assembly of aligned,opposing extensions 1804 with spinous process shelves 1808 lyingside-by-side in the same plane with a gap between them to permit tissuegrowth between the shelves. A joint cylinder 1813 includes a threadedaxial bore 1814 along the longitudinal axis of the joint cylinder andmultiple transverse bores transverse to the axial bore 1814 andextending through the joint cylinder 1813 sidewall. The transverse boresinclude an inboard transverse bore 1816 and outboard transverse bores1818 on either side of the inboard transverse bore 1816. The inboardtransverse bore 1816 is sized to receive the cross bar 1802 in closefitting sliding relationship. The outboard transverse bores 1818 aresized to receive the extension rods 1810 loosely to permit the extensionrods 1810 to toggle in the bores.

The modular implant 1800 is assembled by placing a joint cylinder 1813on each end of a cross bar 1802 with the cross bar 1802 extendingthrough the inboard bore 1816 of each joint cylinder 1813. Twocross-drilled balls 1820 are next inserted into the axial bore 1814 ofeach joint cylinder 1813 and aligned with the outboard bores 1818. Twoextensions are mounted to each joint cylinder 1813 by inserting theextension rod 1810 of each extension into the outboard bores 1818 andthrough the corresponding cross-drilled ball 1820. The cross-drilledballs 1820 are sized to fit closely within the axial bore 1814 and touchthe cross bar 1802. Once assembled, the modular implant 1800 can beadjusted by sliding and rotating the joint cylinders 1813 relative tothe cross bar 1802 and sliding, rotating, and toggling the extensionrods 1810 relative to the joint cylinders 1813. When the desiredadjustment is achieved, a set screw 1822 is inserted into at least oneside of each axial bore 1814 and tightened to compress the cross-drilledballs 1820, extension rods 1810, and cross bar 1802 tightly together andthereby lock the adjustment. In the illustrative example of FIGS. 37-38,the extensions 1804 are all identical, the cross-drilled balls areidentical, and the joint cylinders are identical so that an implant canbe assembled from a few basic components simplifying assembly andreducing inventory costs. However, if desired, a wider variety ofcomponent shapes and sizes may be provided to allow the modular implantto be tailored in various ways.

For example, in FIG. 39, a double ended extension 1824 is providedhaving an extension rod 1826 extending superiorly and another extensionrod 1828 extending inferiorly. By using the double ended extension 1824as a joiner, the modular implant can be assembled to treat multipleadjacent spinal levels. In the illustrative example of FIG. 39, theimplant has been assembled using the double ended extension 1824 toengage three adjacent spinous processes and thus treat two adjacentspinal levels. However, any number of extensions can be assembled inthis manner to treat any number of spinal levels. In addition tocomponents, such as the double ended extension 1824, to allow treatmentof multiple levels, component may be provided that are adapted toparticular bone geometries. For example, extensions having flared spikedpads, extra long spikes, and screw receiving holes similar to theexamples of FIGS. 31-36 may be provided, for example, to permit assemblyof an implant with an inferior portion suitable for gripping a vertebrawith a small or missing spinous process, such as, for example, thesacrum.

Referring to FIG. 40, an implant 1900 similar to that of FIGS. 37-39 isillustrated. The implant 1900 includes extensions 1902 having flattenedspikes 1904.

Referring to FIGS. 41-42, an implant 1950 similar to those of FIGS.37-40 is illustrated. However, in the illustrative example of FIGS.41-42, the extension 1952 includes an extension rod 1954 and spiked pads1956 mounted for translation and rotation along the extension rod 1954.Each spiked pad 1956 is mounted to an extension rod 1954 with a crossdrilled sphere 1958 and a split yoke 1960. The cross drilled sphere 1958is slipped over an end of the extension rod 1954 and a first end of thesplit yoke 1960 is snapped over the cross-drilled sphere 1958 so thatthe cross-drilled sphere 1958 rides in a groove 1962 inside the splityoke 1960. A second end of the split yoke 1960 is mounted in a bore 1964in the spiked pad 1956. The outer surface of the split yoke 1960includes a tapered portion 1966 adjacent the mounting of the split yoke1960 in the bore 1964. The extension rod 1954 is mounted to the crossbar 1968 with joint cylinders 1970 similar to those of the examples ofFIGS. 37-40. When the joint cylinders 1970 are slid medially to engagethe spiked pads 1956 with the spinous processes, each spiked pad 1956 ispressed outwardly toward the extension rod 1954. The edges of the bore1964 slide against the tapered surface 1966 and squeeze the split yoke1960 closed so that it is compressed around the cross-drilled sphere1958 and extension rod 1954 and locks the relative position of thespiked pad 1956 and extension rod 1954. Referring to FIG. 43, an implant2000 includes spiked pads 2002, extension rods 2004, and cross bars2006. Each spiked pad 2002 has a spiked face 2008 and an opposite side2010 having a least one spherical socket 2012 formed in it. In theillustrative example of FIG. 43, each spiked pad 2002 has two sphericalsockets 2012 to permit multi-level constructs as described below. Eachextension rod 2004 includes a spherical ball end 2014 formed at each ofits ends. The cross bar 2006 includes a longitudinal slot 2016 dividingthe cross bar 2006 into two cantilevered beams 2018 joined at a firstend 2020 and threaded at a second end 2022 for receiving a retaining nut2024. The implant 2000 is assembled by snapping a spiked pad 2002 ontoeach end or each of two extension rods 2004 and placing the extensionrods 2004 in the slot of the cross bar 2006. The nut 2024 is threadedonto the end of the extension rod and threadingly advanced to move theextension rods 2004 closer together and compress the spiked pads againstthe spinous processes. Additional spinal levels may be accommodated bysnapping additional extension rods into the second holes of spiked pads,snapping additional spiked pads 2002 to the free end of the additionalrods and compressing the additional assembly with an additional crossbar and nut as shown in FIG. 43.

Referring to FIG. 44, an implant 2100 includes a spacer 2102 including asuperior bar 2104, and inferior bar 2106, and anterior bar 2108, and aposterior bar 2110. Gaps 2112, or fenestrations, between the bars permittissue growth between the bars and receive extension rods 2114 extendingfrom spiked pads 2116. In the illustrative example of FIG. 44, fourindependent spiked pads 2116 are provided. Two of the spiked pads 2116are supported by insertion of their extension rods 2114 betweenposterior surfaces 2118 of the superior and inferior bars and ananterior surface 2120 of the posterior bar. Two of the spike pads 2116are supported by insertion of their extension rods 2114 between anteriorsurfaces 2122 of the superior and inferior bars and a posterior surface2124 of the anterior bar. A bolt 2126 extends from the anterior bar 2108through a bore 2128 in the posterior bar 2110 and is secured with a nut2130. Tightening the nut 2130 compresses the bars and extension poststogether to lock the position of the spiked pads 2116. Loosening the nut2130 allows independent adjustment of each spiked pad 2116medially-laterally 2132, superiorly-inferiorly 2134, angularly 2136, androtationally 2138.

Referring to FIGS. 45-47, a portion of an implant 2200 is shown toillustrate a mechanism for providing an adjustable height spacer 2202having a superior bar 2204 and an inferior bar 2206. The 2204, 2206 barsinclude longitudinal serrations on their anterior sides 2208 andposterior sides 2210. The bars 2204, 2206 are received in a firstsuperiorly-inferiorly elongated slot 2212 formed in an extension 2214.The first slot 2212 includes anterior serrations 2216 engageable withthe anterior serrations 2208 of the bars 2204, 2206 to support the barsin a selected superior-inferior position. A second superiorly-inferiorlyelongated slot 2218 is formed in the extension 2214 transverse to thefirst slot 2212. The second slot 2218 includes opposed hemi-cylindricalthreaded concavities 2220 formed in its sidewalls and directed towardthe first slot 2212. The second slot 2218 receives a lock block 2222 insliding relationship toward the first slot 2212 and the threadedconcavities 2220 receive a lock screw 2224 in threaded relationship. Thelock block 2222 includes anterior facing serrations 2223 engageable withthe posterior serrations 2210 of the bars 2204, 2206. In use, the bars2204, 2206 and extension 2214 are engaged with the bars 2204, 2206received in the first slot 2212. The bars 2204, 2206 are adjustedsuperiorly-inferiorly and medially-laterally within the first slot 2212to a desired position relative to the extension 2214. The lock screw2224 is then rotated causing the lock screw to advance toward the firstslot 2212 and drive the lock block 2222 toward the first slot 2212. Thelock block 2222 presses against the bars 2204, 2206 causing theserrations of the lock block 2222, bars 2204 and 2206, and first slot2212 to engage and lock the desired relative position between theextension 2214 and rods 2204, 2206. Alternatively, the serrations may beomitted and locking accomplished by frictional engagement.

The mechanism of FIG. 44 may be substituted in the preceding examples.For example the mechanism of FIG. 44 may be substituted in the implant100 of FIGS. 1-9 to provide implant 100 with an adjustable heightspacer.

Referring to FIGS. 48-49, an implant 2300 suitable for treating multiplespinal levels includes multiple spacers 2302, 2304 and first and secondunitary, multilevel extensions 2306. Each spacer includes an elongated,hollow, body having a non-circular cross-sectional shape (FIG. 49). Eachspacer further includes at each end a first slot 2310 formed through itssidewall and extending a short distance longitudinally toward theopposite end of the spacer to an inboard end of the first slot. Eachspacer further includes a second slot (not shown) formed through itssidewall and extending circumferentially from the inboard end of eachfirst slot 2310 to a third slot 2312. In the illustrative example ofFIGS. 48-49, the first slot 2310 is formed in a relatively narrow side2314 of the non-circular spacer and the third slot 2312 is formed in arelatively wide side 2316 of the non-circular spacer, the sides beingapproximately ninety degrees apart (FIG. 49). A cylindrical nut 2318 isprovided to fit inside the hollow body at each end of each spacer 2302.The nut 2318 includes a threaded cross-bore 2320. The extensions 2306each include a generally flat, medially facing surface 2322 havingmultiple spiked regions 2324, 2326, 2328 and a flange 2330 extendinglaterally from the extension 2306. Each flange 2330 includessuperiorly-inferiorly elongated holes 2332 extending through the flange2330 from a posterior surface 2334 to an anterior surface 2336. Lockbolts 2338 are provided to join the extensions 2306 to the spacers 2302,2304. In use, the lock bolts 2338 are extended through the flanges 2330and a nut 2318 is loosely threaded onto each bolt. The spacers 2302,2304 are placed between adjacent spinous processes initially with theirnarrow dimension opposing the spinous processes as shown with thesuperior spacer 2302 in FIG. 49. The extensions 2306 are positioned onopposite sides of the spinous processes and the nuts 2318 are slippedinto the hollow interior of the spacers with the bolts 2338 slidingthrough the first slot as shown with the superior spacer 2302 in FIG.49. The elongated holes 2332 in the flanges 2330 permitssuperior-inferior adjustment of the spacers 2302, 2304 relative to theextensions 2306. The spacers 2302, 2304 are then rotated to positiontheir wide dimension opposing the spinous processes as shown with theinferior spacer 2304 in FIG. 49. This rotation may be accomplished forexample by engaging an instrument with the first slit to apply a torqueto the spacer. Rotation of the spacers 2302, 2304 causes the spinousprocesses to move apart as the wide dimension of the spacers is rotatedbetween the spinous processes. As the spacers rotate, the bolts 2338slide through the second slot (not shown) until they are aligned withthe third slot 2312 in the spacer. The extensions 2306 are nowcompressed medially to engage the spikes with the spinous processes. Thebolts 2338 slide within the third slot 2312 during compression. Once thebolts move inward of the second slots, the spacers are prevented fromrotating back by the bolts 2338 abutting the sides of the third slot2312. The bolts 2338 are tightened to lock the position of the spacers2302, 2304 relative to the extensions 2306.

While a specific illustrative example and use of implant 2300 has beenshown and described, it is to be understood that implant 2300 can beassembled in any order. For example, the nuts 2318 may first be slippedinto the spacers 2302, 2304, the spacers placed between the spinousprocesses in a desired final position, the extensions 2306 compressedmedially into the spinous processes, and then the bolts 2338 insertedand tightened. Likewise, while implant 2300 has been shown to treat twospinal levels, it can be readily modified to treat one, three, four,five or any number of spinal levels. Likewise, while the spacers 2302,2304 have been shown with two different dimensions and being rotated tofacilitate distraction of the spinous processes, the spacers 2302, 2304may be inserted without rotation and may have, for example, a singleslot for receiving bolts 2338.

Referring to FIGS. 50-51, an implant 2400, similar to that of FIGS. 1-9,further includes a separate member 2402, 2403 engageable with the spacer2404 to be positioned between adjacent vertebrae. The separate member2402, 2403 may be used to provide additional structural support, toprovide bone growth promoting material, or both. The member 2402, 2403may be made of metal, plastic, bone, ceramic, or any other suitablematerial. For example, the member 2402, 2403 may be a structural bonegraft that both contributes to the support of the spacing betweenadjacent vertebrae and provides bone growth promoting minerals andscaffolding to the surgical site. Also, for example, the member 2402,2403 may be coupled to the spacer to provide additional materialanterior of the spacer. The member 2402, 2403 may be sized smaller(superiorly-inferiorly) than the spacer 2404 so that it bears little, ifany of the load of adjacent vertebrae. Or, the member 2402, 2403 may besized similarly to the spacer 2404 so that it shares the load ofadjacent vertebrae. Or, the member 2402, 2403 may be sized larger thanthe spacer 2404 so that it bears most, or all, of the load of adjacentvertebrae. For, example, the member 2402, 2403 may be a structuralallograft bone member that is sized slightly larger than the spacer 2404to bear the load of adjacent vertebrae to encourage bone growth.However, if the member 2402, 2403 were to resorb or subside, theadjacent vertebrae would then be safely supported by the spacer 2404.Referring to FIG. 50, the member 2402 is generally in the form of aplate-like body having a superior surface 2406, an inferior surface2408, a convex anterior surface 2410, and generally flat posteriorsurface 2412 and a posteriorly projecting connecting member 2414. Theconnecting member includes a base 2416 joined to the posterior surface2412 tapering to a neck 2418 connected to an expanded engagement end2420. The engagement end 2420 has a cross-sectional shape correspondingto the cross sectional shape of the interior 2422 of the spacer 2404. Inuse, the member 2402 is coupled to the spacer 2404 by sliding theengagement end 2420 into the interior 2422 of the spacer 2404, with theneck 2418 sliding within an anteriorly opening slot 2424 of the spacer2404. While the member 2402 is shown in use to augment the anterior sideof the spacer 2404, it may be configured to augment any one or multiplesides of the spacer 2404.

Referring to FIG. 51, the member 2403 is similar to member 2402 of FIG.50 except that instead of engaging the interior of the spacer 2404 itengages the exterior of the spacer 2404 with a ring-shaped engagementmember 2450 that slides over the spacer 2404. In addition, the member2403 includes chamfers 2452 at each end to provide clearance forportions of the vertebrae such as, for example, the facet joints.

Referring to FIGS. 52-53, a set 2600 of instruments for distracting orcompressing adjacent vertebrae away from or toward one another and forcompressing implant extensions medially toward the spinous processes isillustrated. The set 2600 includes a pair of Kocher-style bone clamps2602 having a scissor-like action with a handle end 2604 and a workingend 2606 terminating in bone gripping tips 2608. A Caspar-stylecompressor/distracter 2610 includes arms 2612 joined by a rack 2614extending from one arm and engaging a gear assembly 2616 mounted onanother arm. A knob 2618 is responsive to rotation to rotate a pinion(not shown) relative to the rack 2614 and cause the rack to translate.Rotation of the knob 2618 in a first direction causes the arms 2612 tomove away from one another and rotation of the knob 2618 in an oppositedirection causes the arms 2612 to move toward one another. The arms 2612terminate in arm clamps 2620 able to receive the Kocher-style boneclamps 2602. The set 2600 further includes implant compressors 2624having a scissor-like action with a handle end 2626 and a working end2628 terminating in implant gripping tips 2630.

In use, an implant 100 is positioned with spacer between adjacentspinous processes 2650 and extensions on each side of the spinousprocesses 2650. The bone clamps 2602 are clamped to the vertebrae. Forexample, they are clamped to adjacent spinous processes 2650. The armclamps 2620 of the compressor/distracter are attached to the bone clamps2602. The knob 2618 is then rotated to compress or distract the arms2612, and by extension the bone clamps 2602, until the vertebrae are ina desired relative spacing. The implant compressors 2624 are thenengaged with the implant 100 and compressed to cause the extensions ofthe implant to engage the spinous processes to secure the desiredspacing between the vertebrae.

Referring to FIGS. 54-56, an alternative tip configuration 2700 for theimplant compressor 2624 of FIGS. 52-53 is illustrated. The tips 2700include extensions 2702 having a profile contoured to generally matchthe posterior profile of the implant extensions 2704 to distributecompressive forces over the surface of the implant extensions 2704. Thecompressor extensions 2702 taper toward their superior and inferioraspects 2706, 2708 to minimize the space needed superiorly andinferiorly for tip insertion and to decrease the amount of the surgicalview that is obstructed by the tips. Where the implant includes a setscrew bore 2710, the extension 2702 and arm 2710 may include a relievedportion 2712 aligned with the set screw bore 2710 to permit driving aset screw in the bore 2710.

Referring to FIG. 57, an implant inserter 2800 is useful for insertingan implant 100 similar to that of FIGS. 1-9 in a direct posteriorapproach. The inserter 2800 includes a first arm 2802 and a second arm2804 joined in a scissor-like arrangement and having a handle 2806 endand a working end 2808. The working end of each arm 2802, 2804 includesa clamping face 2810, 2812 movable toward and away from one another inresponse to movement of the working end of the arms toward and away fromone another. The clamping faces 2810, 2812 are operable to clamp, andthereby grip, the first extension 126 of the implant 100. The first arm2802 includes a foot 2814 projecting medially from first end 2816 nearthe clamping faces 2810, 2812 to a second end 2818 spaced from theclamping faces 2810, 2812. The foot 2814 is positionable over the spacer102 when the clamping faces 2810, 2812 are in clamping engagement withthe first extension 126. A slot 2820 is formed near the second end 2818of the foot 2814 and extends posteriorly from an anterior edge 2822 ofthe foot 2814. The slot 2820 is sized to receive the second extension128.

In use, the second extension 128 is placed on the spacer 102 and theinserter 2800 is engaged with the implant by positioning the foot overthe spacer 102 such that the slot 2820 receives the second extension 128and the clamping faces 2810, 2812 are on opposite sides of the firstextension 126. The inserter handles 2806 are operated to clamp the firstextension 126. Thus clamped, the first and second extensions 126, 128are held securely in a predetermined spaced relationship. If desired,the set screw 130 (FIG. 3) may be inserted and tightened to furthersecure the second extension 128 in anticipation of eventual removal ofthe inserter 2800. A relief cut 2824 through the foot 2814posteriorly-to-anteriorly is aligned with the set screw bore tofacilitate operation of the set screw while the implant 100 is engagedwith the inserter. The inserter 2800 may be used to insert the implant100 in a direct posterior-to-anterior direction between adjacent spinousprocesses. The superior and inferior aspects 2826, 2828 of the loot 2814may be relieved to avoid tissue impingement on the foot 2814 and toimprove visualization.

Referring to FIG. 58, a rasp 2900 is provided for rasping adjacenttissues, for example, for removing tissue between adjacent spinousprocesses in preparation for insertion of the implant 100. The rasp 2900includes head 2901 having a conical tip 2902 to aid insertion and teeth2904, insertion and removal of the rasp head 2901 along its longitudinalaxis and rotation of the rasp head 2901 about its longitudinal axis 2906will remove abutting tissue. In the case of its use to prepare adjacentspinous processes, an angled handle 2908, for example forming an angle2910 in the range of 135 to 45 degrees, more preferably in the range of120 to 60 degrees, more preferably at about 90 degrees, is useful toposition the head 2901 between the spinous processes and rotate it backand forth about its axis to abrade tissue. The teeth 2904 are angledtoward the handle 2908 to ease the initial insertion of the head 2901.The angled teeth 2904 are less prone to snagging upon insertion.

Although examples of a spinous process implant and associatedinstruments and techniques have been described and illustrated indetail, it is to be understood that the same is intended by way ofillustration and example only and is not to be taken by way oflimitation. Accordingly, variations in and modifications to the spinousprocess implant, instruments, and technique will be apparent to those ofordinary skill in the art, and the following claims are intended tocover all such modifications and equivalents.

What is claimed is:
 1. An implant for placement between spinousprocesses of adjacent vertebrae of a spine, the implant comprising: aspacer with a first end, a second end, and a longitudinal axis extendingfrom the first end to the second end, the spacer having a sidewallextending longitudinally and having superior and inferior surfacesoperable to abut the spinous processes and maintain the spinousprocesses in spaced apart relationship, the superior and inferiorsurfaces being spaced apart a distance corresponding to a predeterminedminimum spacing between the spinous processes, the spacer having alength extending medially-laterally and a height extendingsuperiorly-inferiorly such that the spacer further includes: acylindrical path extending along the length, the cylindrical pathdefining a cylinder with a circular cross-sectional shape, a slotopening posteriorly on the cylindrical path, and a bolt including aspherical tip slidingly disposed within the cylindrical path and athreaded shaft extending from the slot; and a first extension projectingfrom the spacer transverse to the longitudinal axis to lie generallyalongside the spinous processes of adjacent vertebrae, wherein asuperior portion of the first extension forms a first surface facing asuperior spinous process and an inferior portion of the first extensionforms a second surface facing an inferior spinous process such that thesecond surface is non-coplanar with the first surface, the firstextension being engageable with the spinous processes to limit themaximum spacing between the spinous processes, the first extensionincluding a threaded bore, such that the first extension is connected tothe spacer by threading the bolt into the threaded bore.
 2. The implantof claim 1, further comprising at least one fastener on the inferiorportion of the first extension wherein the second surface of theinferior portion is adapted to direct the at least one fastener intobone.
 3. The implant of claim 1, further comprising at least onefastener and wherein the second surface of the inferior portioncomprises a bore such that the at least one fastener is removablycoupled to the bore and adapted to engage bone.
 4. The implant of claim3, wherein the fastener comprises a bone screw.
 5. The implant of claim4, wherein the bone screw is adapted to engage the sacrum.
 6. Theimplant of claim 1, further comprising a plurality of fasteners whereinat least one of the plurality of fasteners resides on the second surfaceof the inferior portion and at least one of the plurality of fastenersresides on the first surface of the superior portion such that the atleast one fastener residing on the second surface is angled andnon-parallel with the at least one fastener residing on the first planarsurface, and wherein the first surface and the second surface areadapted to direct the plurality of fasteners into bone.
 7. The implantof claim 2, wherein the at least one fastener is adjustable angularlyrelative to the second surface of the inferior portion of the firstextension such that the at least one fastener is non-normal with thesecond surface of the inferior portion.
 8. The implant of claim 1,wherein the superior portion and the inferior portions are offsetanteriorly-posteriorly relative to one another to define a generally“Z”-shaped offset such that the inferior portion extends furtherposteriorly than the superior portion extends anteriorly.
 9. The implantof claim 1, further comprising a second extension opposing the firstextension wherein the second extension is adapted to lie generallyalongside the spinous processes of adjacent vertebrae on an oppositeside of the first extension.
 10. The implant of claim 9, wherein thesecond extension directly engages the spacer and is translated over thespacer toward the first extension.
 11. The implant of claim 9, whereinthe second extension comprises a superior portion forming a thirdsurface and an inferior portion forming a fourth surface such that thefourth surface is non-coplanar with the third surface.
 12. The implantof claim 1, wherein the second surface is substantially perpendicular tothe longitudinal axis.
 13. The implant of claim 1, wherein the firstsurface is substantially perpendicular to the longitudinal axis.
 14. Theimplant of claim 1, wherein the superior portion and the inferiorportion are coupled by a portion of the first extension extendingbetween the superior portion and the inferior portion.
 15. An implantfor placement between spinous processes of adjacent vertebrae of aspine, the implant comprising: a spacer with a first end, a second end,and a longitudinal axis extending from the first end to the second end,the spacer having a sidewall extending longitudinally and havingsuperior and inferior surfaces operable to abut the spinous processesand maintain the spinous processes in a spaced apart relationship, atleast a first superior opening in the spacer and at least a firstinferior opening in the spacer the superior and inferior surfaces beingspaced apart a distance corresponding to a predetermined minimum spacingbetween the spinous processes, the spacer further including: acylindrical path extending along the length, the cylindrical pathdefining a cylinder with a circular cross-sectional shape, a slotopening posteriorly on the cylindrical path, and a bolt including aspherical tip slidingly disposed within the cylindrical path and athreaded shaft extending from the slot; a first extension attached tothe spacer, the first extension including a threaded bore, such that thefirst extension is connected to the spacer by threading the bolt intothe threaded bore.
 16. The implant of claim 15, further comprising asecond extension attached to the spacer and engageable with the spinousprocesses to limit a maximum spacing between the spinous processes, thefirst and second extensions each including a superior portion and aninferior portion, the superior portion of the first extension defining afirst plane and the inferior portion of the first extension defining asecond plane non-coplanar to the first plane, the superior portion ofthe second extension defining a third plane and the inferior portion ofthe second extension defining a fourth plane non-coplanar to the thirdplane, wherein the inferior portion of the second extension divergesfrom the inferior portion of the first extension in an inferiordirection.
 17. The implant of claim 15, further comprising a secondextension attached to the spacer, the first and second extensions eachincluding a superior portion and an inferior portion, the inferiorportions of the first and second extensions each including at least onefastener, wherein the inferior portions are adapted to direct the atleast one fastener into bone.
 18. The implant of claim 15, wherein atleast one of the first superior opening and the first inferior openingincludes a transverse passageway through the spacer.
 19. The implant ofclaim 18, wherein the spacer is substantially hollow and the transversepassageway is formed by the hollow spacer.
 20. The implant of claim 17,wherein the at least one fastener on the inferior portion of the firstextension and the at least one fastener on the inferior portion of thesecond extension converge.
 21. The implant of claim 15, furthercomprising a second extension attached to the spacer, the first andsecond extensions each including an inferior portion, wherein theinferior portions of the first and second extension are adapted toengage a sacrum.
 22. The implant of claim 15, further comprising asecond extension attached to the spacer, the first and second extensionseach including an inferior portion, wherein the inferior portions of thefirst and second extensions are adapted to engage a bone having a smallspinous process relative to an adjacent spinous process.
 23. The implantof claim 15, further comprising a second extension attached to thespacer, the first and second extensions each including an inferiorportion, wherein the inferior portions of the first and secondextensions are adapted to engage a lamina.
 24. A method of treatingspine disease comprising: providing a spacer with a first end, a secondend, and a longitudinal axis extending from the first end to the secondend, the spacer having a sidewall extending longitudinally and havingsuperior and inferior surfaces operable to abut adjacent spinousprocesses and maintain the spinous processes in a spaced apartrelationship, the superior and inferior surfaces being spaced apart adistance corresponding to a predetermined minimum spacing between thespinous processes; a first extension projecting from the spacertransverse to the longitudinal axis to lie generally alongside thespinous processes of adjacent vertebrae, the first extension having athreaded bore, a superior portion and an inferior portion where part ofthe inferior portion is angled and non-parallel with respect to thesuperior portion, the first extension being engageable with the spinousprocesses to limit the maximum spacing between the spinous processes;and a second extension to lie generally alongside the spinous processesof adjacent vertebrae on a side opposite the first extension, the secondextension having a superior portion and an inferior portion where partof the inferior portion is angled and non-parallel with respect to thesuperior portion, the second extension being engageable with the spinousprocesses to limit the maximum spacing between the spinous processes,the spacer having a length extending medially-laterally and a heightextending superiorly-inferiorly such that the spacer further includes: acylindrical path extending along the length, the cylindrical pathdefining a cylinder with a circular cross-sectional shape, a slotopening posteriorly on the cylindrical path, and a bolt including aspherical tip slidingly disposed within the cylindrical path and athreaded shaft extending from the slot; inserting the spacer betweenspinous processes of adjacent vertebrae to provide both an extensionstop and a flexion stop; engaging the second extension to the spacer;threading the bolt into the threaded bore; translating the secondextension axially towards the first extension so as to slide the secondextension toward the first extension so the first and second extensionsengage with the spinous processes to fix the spacer to the spinousprocesses; and securing the second extension at a desired location alongthe spacer relative to the first extension.
 25. The method of claim 24,wherein the spacer further comprises a plurality of fasteners wherein atleast one of the plurality of fasteners resides on the part of theinferior portion of the first extension and at least another of theplurality of fasteners resides on the part of the inferior portion ofthe second extension, and wherein the translating step comprisesengaging the at least one and the at least another of the plurality offasteners with a sacrum.